1. Field of the invention
The present invention relates to a scene change detector, and in particular to a scene change detector capable of detecting very fast and accurately a scene change for classifying scenes in video retrieval.
2. Description of the Related Art
Scene changes, which include not only an abrupt scene change, at which scene changes instantaneously, but also special effects such as dissolve and wipe.
As methods for detecting an abrupt scene change, there are methods of using a great change of a statistical characteristic, such as luminance components, motion, and so on. According to, for example, xe2x80x9cA Fast Detecting Method of Scene Breaks from MPEG Encoded Moviesxe2x80x9d, Kaneko, Hori, Information Processing Society of Japan, Annual Convention, 5N-2 (1997), the bit amount of motion vectors is used to measure a similarity between frames, and if the peak of the similarity is detected an abrupt scene change is detected. Moreover, according to xe2x80x9cA Scene Cut Detection from Compressed Video using Interframe Luminance Difference and Chrominance Correlationxe2x80x9d, Nakajima, Institute of Electronics, Information and Communication Engineers, Spring Conference, D-501 (1994), data on discrete frames are used to combine temporal peaks of the luminance inter-frame differences and chrominance histogram correlation, so that an abrupt scene change is detected.
A decision of a flashlight scene, which may often be regarded as an abrupt scene change, is given by examining the correlation between continues plural frames. For example, Japanese Patent Application No. 9-041709 discloses that the correlation between the current frame n (n is a positive integer), which is currently used for cut detection, and the frame (nxe2x88x921), and the correlation between the frame (n+1) and the frame (nxe2x88x921) are examined; and then in the case that it is declared that there is an abrupt scene change between the former two frames but there is not an abrupt scene change between the latter two frames, the current frame n is judged as a flashlight scene.
Since special effects such as dissolve, fade-in/fade-out, and wipe are transitions continuing for a certain period, they can be judged by continuously observing a certain characteristic value of pixel domains, such as a change of luminance or inter-frame difference. For example, Japanese Patent Application No. 8-252333 discloses, as a method of using reduced size images, that the moving average of inter-frame activity is obtained from the frame activity, of luminance components of each frame, and further the correlation between the frames in a chrominance histogram is obtained from a histogram of chrominance signals of each frame, and in the case that their temporal changes exceed each predetermined threshold, it is judged that the scene change is dissolve. As an example of using coding parameters, apart from this, xe2x80x9cScene Change Detection from MPEG coded dataxe2x80x9d Niikura, Taniguti, Tomura, et al., Institute of Electronics, Information and Communication Engineers, Technical Report, IE97-65 (1997) reports that dissolve transition is detected by using the characteristic that during dissolve transition prediction errors become relatively large and their signs remain constant.
Concerning judgment of wipe, as an example of detecting wipe from reduced size images, Japanese Patent Application No. 9-041709 discloses that in the case that the number of frames whose inter-frame differential values in a certain period exceed a first threshold is larger than a second threshold and in addition the number of frames whose inter-frame differential values in periods before and after the above-mentioned period are smaller than a third threshold is larger than a fourth threshold, it is judged that the above-mentioned period is wipe. To the contrary, there has been very few report about wipe detection on coding parameters domain.
The scene change detection methods in the above-mentioned prior art have the following problems. The method of preparing reduced size images as a pre-processing of cut detection has a problem that particularly when the size of an image becomes large, processing costs in a reduced size image reconstructor cannot be ignored and the fast operation for cut detection cannot be realized. For example, in case of processing standard TV size of video, it takes almost the same time as realtime playback of compressed data.
The method of using the change of statistical characteristic between reconstructed small size images to detect a scene change has a problem that it is necessary to hold decoded frames and similarly device costs increase when the size of images becomes large.
The method using only intra-coded frames in order to reduce detection-process has a problem that because these are temporally distributed even such a scene where a camera or an object is moving may be incorrectly detected as a scene change.
The cut detection method of using a coding parameter obtained by variable-length-decoding compressed video data needs to extract the coding parameters of all blocks, and thus has a problem that in the case that the size of images becomes larger, an increase in detection time is caused. As for an image of, for example, a standard TV size, only about 1.4 times as fast operation as play backing compressed data can be realized.
Furthermore, in the case of detecting special effect such as dissolve and wipe on coding parameter domain parameter, it is difficult to detect such a special effect accurately. Thus, there remains a problem about reliability.
An object of the present invention is to provide a scene change detector capable of detecting scene changes including special effects such as dissolve or wipe at high speed and accuracy by a processing which is far less than that of conventional scene change detectors.
The present invention has the following characteristics: the present invention comprises a means for video-signal-demultiplexing compressed moving pictures data, a means for extracting at least predictive-coded mode information, motion vectors, and coded transformed coefficients from the video-signal-demultiplexed information obtained by the above-mentioned means, and a means for judging scene changes by using the extracted predictive-coded mode information, the motion vector, and the coded transformed coefficients.
The present invention makes a high speed processing possible by using, for judgment of scene changes, coding parameters obtained from video-signal-demultiplexing which is the minimum decoding process; the present invention also makes it possible to detect scene changes at a higher speed, as compared with conventional scene change detectors using coding parameters, by greatly cutting down blocks from which coding parameters should be extracted temporally and spatially.
In the present invention, it is unnecessary to apply complicated operation to the extracted coding parameters. And thus a scene change can be detected by simple thresholding process and multiplication/addition operation so that device costs can be reduced to a great extent.
The present invention also makes it possible to determine, in detecting an abrupt scene change where scenes change instantaneously, the abrupt scene change by using only predictive-coded mode information of blocks in a frame which is temporally and spatially subsampled.
In the present invention, in the case that plural frames judged as abrupt scene changes are temporally concentrated, it is judged that these frames belong to a flashlight scene so as to be excluded from the candidate of abrupt scene changes.
The present invention also makes it possible to detect special effects such as dissolve, fade-in, and fade-out, which has been entrusted to the judgment on pixel domains up to the present, by motion information and prediction error information of pictures calculated from coding parameters, thereby distinguishing them from a still scene, and a small motion scene.
The present invention also makes it possible to detect wipe, which has been so far detected by change over time in a statistical characteristic on pixel domains, by motion information and prediction error information of pictures calculated from coding parameters, thereby distinguishing them from scenes where a camera or an object is moving.
According to the present invention, an abrupt scene change and special effects including dissolve and wipe can be detected at very high speed and accuracy from coding parameters, extracted from compressed video data.